In this study, a highly stable time-domain approach for analysing the ion-flow field of the bipolar high-voltage direct current transmission lines is proposed. The influence of the space charges generated by corona on the electric field is taken into account. Usually, the steady state of this electric field space charge coupled problem is directly solved and the transient process is ignored. However, the complete time-domain analysis of this problem may provide a deep look at the formation process of the direct current ion-flow field. In this work, the charge simulation method is used to solve the space-charge-free electric field, the finite element method is employed to solve the electric field in the presence of space charges, and the finite volume method is applied to solve the current continuity equation. Crank-Nicolson method is introduced to separate the governing equations in time domain and overcome the time-step limitation. Good agreement is obtained between the calculated and experimental results, verifying the validity of the approach.